Presentation of the tools developed (part 2)

How to merge data and models using LAVA?

-> Annalisa GRIFFA, CNR-ISMAR

Presentation of the tools developed (part 2)

Knowing the ocean currents and their transport is crucial in SAR and oil spill operations. Even small errors in the velocity field can cause significant errors in transport estimates

Numerical prediction models provide estimates of velocity fields in many areas, but they can have significant errors especially in highly variable coastal flows

HF coastal radars are more accurate, but they are available only in a few areas

Floating instruments like drifters can be launched in case of accidents and provide direct transport measurements, but their coverage is limited.

The LAVA software allows to combine information from models, radars and drifters, optimizing estimates of transport

LAVA has been originally developed in collaboration between various institutions (CNR-ISMAR, MIO, LOV, University of Miami) and it has been thoroughly tested in a number of scientific publications (Molcard et al., 2003; Taillandier et al., 2006, 2008;2010; Chang et al., 2011)

In TOSCA, LAVA has been customized, made user friendly and inserted in the GIS as a demo for the Toulon experiment. Information can be found at http://toscagis.univ-tln.fr/TOSCA/squel.php?content=playLava2.php

LAVA corrects the velocity fields from models or HF radars using drifter data, requiring minimal distance between the observed drifters and particles simulated in the velocity fields

The LAVA corrected velocities are therefore optimized for transport estimates

LAVA can also be used with drifters only, to reconstruct the velocity field in the area in the proximity of the drifters

The LAVA algorithm

LAVA application during the Toulon experiment

Example of radar coverage (color indicates velocity magnitude) with superimposed drifters (black lines)

During the Toulon experiment in August 2012, an HF radar system and the coastal model GLAZUR64 were active, and 20 drifters have been launched

LAVA has been applied using 7 drifters to correct the HF radar and model velocities during the period 5-10 August

The other 13 drifters have been used to test the results, considering them as proxy for substances transported by the currents.

Model

Radar

Example of drifter trajectory comparison

Green trajectories = without LAVA correction

Purple trajectories = with LAVA correction

Black real drifter trajectories

Quantitative results Radar and model results are significantly improved using LAVA.

Without LAVA, radar already provides satisfactory estimates of transport, with mean errors of 5 km in drifter position in 24 h. Model errors are higher, of order of 10-15 km in 24 h.

With LAVA both radar and model errors are reduced to approximately 2 km in 24 h

We also tested a simple approximation for forecast, keeping the velocity constant and computing trajectories. Some improvements are shown for models during the first few hours

LAVA in an operational context: possible scenarii Scenarios and general suggestions to use LAVA in case of accidents at sea are discussed in the following:

Timely and targeted drifter launches should be included in rapid response actions

LAVA should be run in real-time to correct velocity fields from models and radars using drifter data

If models and radar information are not available, use LAVA with drifters only to reconstruct the velocity field

NOTICE: drifters can be launched by boats or planes involved in rapid response. It might also be advisable to require that a small number of drifters should be carried by cargo and passenger vessels, to be used in case of accidents at sea

A timely launch from the ship could help enormously in case of both SAR and oil spill mitigation operations, correcting and improving model results also in open sea

LAVA: ongoing work Inserted in the TOSCA-GIS as a demo for the Toulon experiment Strong effort to make LAVA as more user-friendly as possible:

a) provide pre-compiled binary files for both 32 and 64bit machines;

b) compiler portability: GNU, Portland Group and Intel Fortran compilers are currently supported

c) different new ASCII input/output file formats, NetCDF format is now supported

d) set up of Wiki-LAVA

Wiki-LAVA is ongoing

General info

Info on how to run LAVA

Thanks for attendingTOSCA Final Meeting!